What is the best way to model the interior of a vehicle as accurate as possible and what source should I use?
The best way to model the inside accurately is to find a reference image of each individual part of that particular bus or any other bus. This way you will have a good reference that isn't warped in any way. You would then model that part and can use it for your bus. The advantage of modeling the part as a separate object means that you can then use that part in other scenes as well.

For example here is a steering wheel reference from a VW Bus: